The invention relates to a controller for controlling opening/closing operation of an electromagnetic valve, and more specifically it relates to a controller for controlling the timing of de-energizing an electromagnet of the electromagnetic valve in accordance with a dead time determined based on known parameters.
An electromagnetic actuator alternately supplies electric power to a pair of opposing electromagnets to drive an armature, which is placed between a pair of opposing springs, between one terminal position and the other terminal position. When the intake/exhaust valves of an internal combustion engine are driven through the electromagnetic actuator, it is possible to control the valve timing variably as compared with a mechanical actuator. The electromagnetic actuator makes it possible to improve the output characteristics and fuel efficiency of an engine. Therefore, it is desired to apply the electromagnetic actuator to the intake/exhaust valves of an engine as a future possibility.
In common electromagnetic valves, an armature which is seated as a result of being attracted by one of the electromagnets is released from the seated state when the one of the electromagnet is de-energized. The armature starts to move toward a neutral position at which the opposing force of each of the two opposing springs balances. At certain timing in synchronization with this movement, electric current is supplied to the other of the electromagnets to attract the armature.
As the armature approaches the other of the electromagnets, the magnetic flux grows abruptly. The work by the attractive force of the other of the electromagnets overcomes the sum of the slight work to draw the armature back by residual magnetic flux of the one of the electromagnets and a mechanical loss. Thus, the armature reaches a seated position of the other electromagnet. As seating takes place, holding current is supplied at an appropriate timing to maintain the armature in the seated position.
In actual valve operation, it is not easy to control the attractive force for maintaining the armature in the seated position, so that there is variation in the residual magnetic flux when the armature is released. As a result, a time period from the time when the electromagnet is de-energized to the time when the armature actually leaves the seated position varies, the time period being referred to as xe2x80x9cdead timexe2x80x9d hereinafter. It is desirable that the dead time has already elapsed by the time when a valve timing command for activating the valve opening/closing operation is actually executed. Otherwise, valve opening/closing operation cannot start quickly in response to the valve timing command, degrading the accuracy of valve timing.
Japanese Patent Application Laid-Open No. 6-2599 discloses a method for correcting a variation of a dead injection time for the fuel injection valve, the dead injection time being defined as a time period from the time when a driving signal is applied to the fuel injection valve to the time when the fuel injection valve is actually opened. According to the method, the dead injection time is determined from the rate of change of current flowing through the fuel injection valve. The timing for opening the fuel injection valve for the current cycle is determined based on the dead injection time determined when the fuel injection valve has been opened in the previous cycle.
The length of the dead time for the electromagnetic actuator varies depending on various parameters such as supplied voltage, engine load, holding current value, engine rotational speed, valve timing, etc. Since the above-mentioned conventional method determines the dead time for the current cycle based on only the dead time for the previous cycle, there may happen a delay in opening/closing valve operation when such parameters abruptly change. Therefore, the method may not achieve a proper engine performance.
There exists a need for an electromagnetic valve controller that determines the dead time more precisely to maintain the accuracy of valve timing.
According to one aspect of the invention, an electromagnetic valve controller for controlling an electromagnetic valve is provided. The controller estimates a dead time based on predetermined parameters. A dead time for the current cycle is determined based on the estimated dead time. An actual de-energization timing for de-energizing an electromagnet of the valve is determined based on the dead time determined for the current cycle. An electromagnet of the valve is de-energized in accordance with the actual de-energization timing. Thus, the accuracy of valve timing is maintained even when driving conditions abruptly change, because the dead time for the current cycle is determined based on the predetermined parameters showing the driving conditions. The predetermine parameter may include engine rotational speed, engine load, supplied voltage, holding current and valve timing.
According to one embodiment of the invention, the electromagnetic valve controller measures a dead time in the previous cycle. A deviation between the dead time measured in the previous cycle and the dead time estimated in the previous cycle is determined. The determined deviation is added to the dead time estimated in the current cycle to determine the dead time for the current cycle. Thus, the accuracy of valve timing is improved because the dead time estimated in the current cycle is corrected with the deviation generated in the previous cycle.
According to another embodiment of the invention, the electromagnetic valve controller further determines a target de-energization timing indicating when to execute a valve timing command, based on predetermined parameters such as valve timing and engine rotational speed. The dead time determined for the current cycle is offset or subtracted from the target de-energization timing to determine the actual de-energization timing. Thus, valve timing is carried out in accordance with driving conditions.